This invention relates in general to method of making a high current density long life cathode for use in high power microwave tube applications and in particular to such a method in which the emitting surface of the cathode is impregnated with a mixture of Ba.sub.3 WO.sub.6, Ba.sub.2 SrWO.sub.6 and ZrH.sub.2.
The state of the art in high power microwave tubes has progressed to the point where the major limiting factor in achieving high power, long life operation is the cathode, which is the heart of the device. Of all the cathodes presently under development, the one that has the best reported emission density as a function of temperature is the tungstate cathode in which the active compound of the emitting surface is Ba.sub.5 Sr(WO.sub.6).sub.2. This cathode is presently made by pressing the tungstate powder into a pellet and machining the surface of the pellet. Though the cathode made by this method is adequate from an emission standpoint, it has several disadvantages. That is, the cathode shapes that can be made by the pressing method are severely limited due to the requirement that extremely high compaction pressures be used in the fabrication of the emitter. Moreover, the cost per emitter is in excess of $300 per cathode. Then too, the cathodes fabricated by the pressing method are hygroscopic and thus quite sensitive to degradation. This necessitates that after firing in hydrogen at 1840.degree. C, the cathodes made by the pressing method must be cooled and immediately stored in a vacuum. Because of this property, cathodes fabricated by pressing are not conducive to fabrication by low cost production methods.